This invention relates to removing contaminants from porous material, and more particularly to removing PCB from porous material, such as wood, paper and polymeric membranes used in the construction of electrical equipment.
Electrical insulating fluids that contain polychlorinated biphenyl (PCB) were once used frequently in electrical transformers, choke coils and capacitors. However, it has been found that these PCB-containing insulating fluids are physiologically and environmentally dangerous, so that the transformers, choke coils and capacitors must be replaced with apparatus that do not contain environmentally harmful insulating fluids. In order to eliminate unusable PCB-containing insulating fluid and PCB-saturated or PCB-moistened solid materials, strict regulations are in effect. For example, many jurisdictions have regulations which only permit destruction in an officially authorized incinerator or storage in an officially authorized hazardous waste dump. In order to minimize this expensive type of disposal elimination, it is desirable for the component parts of the electrical apparatus to be cleaned of PCB to such an extent that they have a PCB content below the maximum set by official regulations.
As is known on the prior art, reducing the level of PCB compounds to a nonhazardous level in a material includes (a) contacting the PCB compound-containing material with an extraction solvent at a temperature and for a time sufficient to remove the absorbed PCB compound; and (b) separating the PCB compound-containing extraction solvent from the material.
U.S. Pat. No. 4,983,222 to Green et al, U.S. Pat. No. 5,203,359 to Fesmire et al and U.S. Pat. No. 4,988,391 to von Bormann, all teach the use of agitation of the material in solvent for decontaminating materials. However, Green et al, Fesmire et al, and von Bormann all teach methods for removing contaminants from non-porous materials only, and that porous material is to be disposed of.
It is particularly difficult to clean the solid porous insulating parts of electrical apparatus. Such insulating substances are formed of insulating paper, insulating press board, resin bonded paper, resin bonded fabric, insulating wood, polypropylene or other polymeric membranes, or synthetic-resin-bonded compressed wood. Since the insulating parts are in contact with the insulating fluid in an electrical appliance, the pores of these insulating parts are thoroughly saturated with PCB-containing insulating medium. Rinsing these insulating substances with a solvent for PCB cannot substantially remove the insulating fluid from deep within the insulating parts, instead it can only clean the surface thereof.
The prior art teaches methods for decontaminating porous materials which are contaminated with various substances, such as PCB. U.S. Pat. No. 4,826,538 to Sanders et al teaches filling and draining with a cleaning solvent repeatedly and agitating the porous material in solution, including rotation around a vertical axis of the porous material in solution, until the desired level of decontamination is obtained. U.S. Pat. No. 3,739,791 to Fry et al also teaches a system for decontaminating various articles which includes rotation about a vertical axis.
The invention provides a method for removing a toxic contaminant from porous material comprising the steps of: (a) placing the material in a drum having a horizontal axis; (b) placing a fluid solvent for the toxic contaminant in the drum; (c) rotating the drum around the horizontal axis for a period of time sufficient for a quantity of the toxic contaminant to mix with the solvent; and (d) subsequently removing the fluid solvent from the drum. The cycle may be repeated until assessment of the quantity of toxic contaminant indicates that a desired quantity of toxic contaminant is obtained. Preferably, the contaminant is a PCB. Preferably, the solvent is selected from the group consisting of n-hexane, xylene, perchloroethylene, tetrachloroethylene, trichlorofluoroethane or any other solvent from the hydrofluoroether family. Preferably, the porous material is selected from the group consisting of electrical insulation materials, soil, sand, natural polymeric materials and synthetic polymeric materials.
Preferred conditions for the invention include a rotation period of 20 to 30 minutes at a speed of between 1 and 10 rotations per minute, and/ or heating the solvent from the ambient temperature to a final temperature from 20 to 50 C. below the boiling temperature of the solvent.
In a preferred embodiment, the invention also contemplates placing the drum in a sealable container and sealing the container subsequent to step (a) and prior to step (b). The present invention also teaches apparatus for carrying out this preferred embodiment, including: a cart containing the drum; a sealable container having a wall and having a door for receiving the cart in the sealable container; fill and drain tubes passing through the wall of the sealable container, the fill and drain tubes capable of releasably attaching to the drum, for filling the drum with solvent and for draining the solvent from the drum; and a motor for rotating the drum and a power generator for supplying power to the motor. Preferably, the motor is located on the cart. Preferably, the power generator is located outside of the sealable container.
In a preferred embodiment, the invention also contemplates a track for receiving and removing the cart from the sealable container. In a further preferred embodiment, a portion of the track which extends beyond the interior of the container is removable.